Cancer is the second most prevalent cause of death in the United States, causing 450,000 deaths per year. While substantial progress has been made in identifying some of the likely environmental and hereditary causes of cancer, there is a need for additional therapeutic modalities that target cancer and related diseases. In particular there is a need for therapeutic methods for treating diseases associated with dysregulated growth/proliferation.
Cancer is a complex disease arising after a selection process for cells with acquired functional capabilities like enhanced survival/resistance towards apoptosis and a limitless proliferative potential. Thus, it is preferred to develop drugs for cancer therapy addressing distinct features of established tumors.
One pathway that has been shown to mediate important survival signals for mammalian cells comprises receptor tyrosine kinases like platelet-derived growth factor receptor (PDGF-R), human epidermal growth factor 2/3 receptor (HER2/3), or the insulin-like growth factor 1 receptor (IGF-1R). After activation the respectives by ligand, these receptors activate the phoshatidylinositol 3-kinase (Pi3K)/Akt pathway. The phoshatidylinositol 3-kinase (Pi3K)/Akt protein kinase pathway is central to the control of cell growth, proliferation and survival, driving progression of tumors. Therefore within the class of serine-threonine specific signalling kinases, Akt (protein kinase B; PKB) with the isoenzmyes Akt1 (PKBα), Akt2 (PKB β) and Akt3 (PKB γ) is of high interest for therapeutic intervention. Akt is mainly activated in a Pi3-kinase dependent manner and the activation is regulated through the tumor suppressor PTEN (phosphatase and tensin homolog), which works essentially as the functional antagonist of Pi3K.
The Pi3K/Akt pathway regulates fundamental cellular functions (e.g. transcription, translation, growth and survival), and is implicated in human diseases including diabetes and cancer. The pathway is frequently overactivated in a wide range of tumor entities like breast and prostate carcinomas. Upregulation can be due to overexpression or constitutively activation of receptor tyrosine kinases (e.g. EGFR, HER2/3), which are upstream and involved in its direct activation, or gain- or loss-of-function mutants of some of the components like loss of PTEN. The pathway is targeted by genomic alterations including mutation, amplification and rearrangement more frequently than any other pathway in human cancer, with the possible exception of the p53 and retinoblastoma pathways. The alterations of the Pi3K/Akt pathway trigger a cascade of biological events, that drive tumor progression, survival, angiogenesis and metastasis.
Activation of Akt kinases promotes increased nutrient uptake, converting cells to a glucose-dependent metabolism that redirects lipid precursors and amino acids to anabolic processes that support cell growth and proliferation. These metabolic phenotype with overactivated Akt lead to malignancies that display a metabolic conversion to aerobic glycolysis (the Warburg effect). In that respect the Pi3K/Akt pathway is discussed to be central for survival despite unfavourable growth conditions such as glucose depletion or hypoxia.
A further aspect of the activated PI3K/Akt pathway is to protect cells from programmed cell death (“apoptosis”) and is hence considered to transduce a survival signal. By acting as a modulator of anti-apoptotic signalling in tumor cells, the Pi3K/Akt pathway, particular Akt itself is a target for cancer therapy. Activated Akt phosphorylates and regulates several targets, e.g. BAD, GSK3 or FKHRL1, that affect different signalling pathways like cell survival, protein synthesis or cell movement. This Pi3K/Akt pathway also plays a major part in resistance of tumor cells to conventional anti-cancer therapies. Blocking the Pi3K/Akt pathway could therefore simultaneously inhibit the proliferation of tumor cells (e.g. via the inhibition of the metabolic effect) and sensitize towards pro-apoptotic agents.
Akt inhibition selectively sensitized tumor cells to apoptotic stimuli like Trail, Campthothecin and Doxorubicin. Dependent on the genetic background/molecular apperations of tumors, Akt inhibitors might induce apoptotic cell death in monotherapy as well.
In the International patent applications WO2004096131, WO2005100344, WO2006036395, WO2006065601, WO2006091395 and WO2006135627 Akt inhibitors are described. In a recent disclosure, Y. Li et al (Bioorg. Med. Chem. Lett. 2009, 19, 834-836 and cited references therein) detail the difficulty in finding optimal Akt inhibitors. The potential application of Akt inhibitors in multiple disease settings, such as for example, cancer, makes the provision of new, alternative Akt inhibitors to those currently available highly desirable.